Lentzea sokolovensis sp. nov., Lentzea kristufekii sp. nov. and Lentzea miocenica sp. nov., rare actinobacteria from Miocene lacustrine sediment of the Sokolov Coal Basin, Czech Republic.

The taxonomic position of three actinobacterial strains, BCCO 10_0061T, BCCO 10_0798T, and BCCO 10_0856T, recovered from bare soil in the Sokolov Coal Basin, Czech Republic, was established using a polyphasic approach. The multilocus sequence analysis based on 100 single-copy genes positioned BCCO 10_0061T in the same cluster as Lentzea waywayandensis, strain BCCO 10_0798T in the same cluster as Lentzea flaviverrucosa, Lentzea californiensis, Lentzea violacea, and Lentzea albidocapillata, and strain BCCO 10_0856T clustered together with Lentzea kentuckyensis and Lentzea alba. Morphological and chemotaxonomic characteristics of these strains support their assignment to the genus Lentzea. In all three strains, MK-9(H4) accounted for more than 80 % of the isoprenoid quinone. The diagnostic diamino acid in the cell-wall peptidoglycan was meso-diaminopimelic acid. The whole-cell sugars were rhamnose, ribose, mannose, glucose, and galactose. The major fatty acids (>10 %) were iso-C15 : 0, anteiso-C15 : 0, iso-C16 : 0, and C16 : 0. The polar lipids were diphosphatidylglycerol, methyl-phosphatidylethanolamine, phosphatidylethanolamine, hydroxy-phosphatidylethanolamine, phosphatidylglycerol, and phosphatidylinositol. The genomic DNA G+C content of strains (mol%) was 68.8 for BCCO 10_0061T, 69.2 for BCCO 10_0798T, and 68.5 for BCCO 10_0856T. The combination of digital DNA-DNA hybridization results, average nucleotide identity values and phenotypic characteristics of BCCO 10_0061T, BCCO 10_0798T, and BCCO 10_0856T distinguishes them from their closely related strains. Bioinformatic analysis of the genome sequences of the strains revealed several biosynthetic gene clusters (BGCs) with identities >50 % to already known clusters, including BGCs for geosmin, coelichelin, ε-poly-l-lysine, and erythromycin-like BGCs. Most of the identified BGCs showed low similarity to known BGCs (<50 %) suggesting their genetic potential for the biosynthesis of novel secondary metabolites. Based on the above results, each strain represents a novel species of the genus Lentzea, for which we propose the name Lentzea sokolovensis sp. nov. for BCCO 10_0061T (=DSM 116175T), Lentzea kristufekii sp. nov. for BCCO 10_0798T (=DSM 116176T), and Lentzea miocenica sp. nov. for BCCO 10_0856T (=DSM 116177T).

Kitasatospora fiedleri sp. nov., a novel antibiotic-producing member of the genus Kitasatospora.

Strain TÜ4103T was originally sampled from Java, Indonesia and deposited in the Tübingen strain collection under the name 'Streptomyces sp.'. The strain was found to be an antibiotic producer as strain TÜ4103T showed bioactivity against Gram-positive bacteria, such as Bacillus subtilis and Kocuria rhizophila in bioassays. Strain TÜ4103T showed 16S rRNA gene sequence similarity of 99.65 % to Kitasatospora cheerisanensis DSM 101999T and 98.82 % to Kitasatospora niigatensis DSM 44781T and Kitasatospora cineracea DSM 44780T. Genome-based phylogenetic analysis revealed that strain TÜ4103T is closely related to K. cineracea DSM 44780T and K. niigatensis DSM 44781T. The digital DNA-DNA hybridization values between the genome sequences of strain TÜ4103T and its closest phylogenomic relatives, strains DSM 44780T and DSM 44781T, were 43.0 and 42.9 %, respectively. Average nucleotide identity (ANI) values support this claim, with the highest ANI score of 91.14 % between TÜ4103T and K. niigatensis being closely followed by an ANI value of 91.10 % between K. cineracea and TÜ4103T. The genome of TÜ4103T has a size of 7.91 Mb with a G+C content of 74.05 mol%. Whole-cell hydrolysates of strain TÜ4103T are rich in meso-diaminopimelic acid, and rhamnose, galactose and mannose are characteristic as whole-cell sugars. The phospholipid profile contains phosphatidylethanolamine, diphosphatidylglycerol and glycophospholipid. The predominant menaquinones (>93.5 %) are MK-9(H8) and MK-9(H6). Based on the phenotypic, genotypic and genomic characteristics, strain TÜ4103T (=DSM 114396T=CECT 30712T) merits recognition as the type strain of a novel species of the genus Kitasatospora, for which the name Kitasatospora fiedleri sp. nov. is proposed.

Nocardia australiensis sp. nov. and Nocardia spumae sp. nov., isolated from sea foam in Queensland, Australia.

Strains USC-21046T and USC-21048T were isolated from foaming coastal marine waters on the Sunshine Coast, Queensland, Australia. Both strains displayed growth and morphological characteristics typical for members belonging to the genus Nocardia. The major polar lipids were diphosphatidylglycerol and phosphatidylethanolamine, and the major fatty acids were C16 : 0, C18 : 1 ω9c, C18 : 0 and C18 : 0 10-methyl. The mycolic acids of strains USC-21046T and USC-21048T consisted of chain lengths between 50-64 and 56-68, respectively. Moreover, both of those strains contained meso-diaminopimelic acid and ribose, arabinose, glucose and galactose as whole cell sugars. Based on the phylogenomic results, both strains belonged to the genus Nocardia with strain USC-21046T showing an 80.4 % genome similarity to N. vinacea NBRC 16497T and N. pseudovaccinii NBRC 100343T, whereas USC-21048T strain showed an 83.6 % genome similarity to N. aobensis NBRC 100429T. Both strains were delineated from their closely related relatives based on physiological (e.g. growth on sole carbon source) and chemotaxonomic (e.g. cellular fatty composition) differences. The digital DNA-DNA hybridization (dDDH) values between USC-21046T and USC-21048T and their closely related relatives were below the dDDH threshold value of ≤70 % used for the taxonomic classification of novel species status. The genome length of strains USC-21046T and USC-21048T were 6 878 863 and 7 066 978 bp, with G+C contents of 65.2 and 67.8 mol%, respectively. For the novel isolates, we propose the names Nocardia australiensis sp. nov. with the type strain USC-21046T (=DSM 111727T=NCCB 100867T) and Nocardia spumae sp. nov. with the type strain USC-21048T (=DSM 111726T=NCCB 100868T).

High Plasticity of the Amicetin Biosynthetic Pathway in Streptomyces sp. SHP 22-7 Led to the Discovery of Streptcytosine P and Cytosaminomycins F and G and Facilitated the Production of 12F-Plicacetin.

A chemical reinvestigation of the Indonesian strain Streptomyces sp. SHP 22-7 led to the isolation of three new pyrimidine nucleosides, along with six known analogues and zincphyrin. The structures of the new compounds (6, 7, 10) were elucidated by employing spectroscopic techniques (NMR, MS, CD, and IR) as well as enantioselective analyses of methyl branched side chain configurations. Application of the precursor-directed feeding approach led to the production and partial isolation of nine further pyrimidine analogues. The new compounds 6, 7, and 11 and three of the known compounds (2-4) were found to possess antimycobacterial and cytotoxic properties.

Kibdelosporangium persicum sp. nov., a new member of the Actinomycetes from a hot desert in Iran.

Isolate 4NS15T was isolated from a neglected arid habitat in Kerman, Iran. The strain showed 16S rRNA gene sequence similarity values of 98.9 % to the type strains of Kibdelosporangium aridum subsp. aridum, Kibdelosporangium phytohabitans and Kibdelosporangium philippinense and 98.6 % to the type strain K. aridum subsp. largum, respectively. Genome-based phylogenetic analysis revealed that isolate 4NS15T is closely related to Kibdelosporangium aridum subsp. aridum DSM 43828T. The digital DNA-DNA hybridization value between the genome sequences of 4NS15T and strain DSM 43828T is 29.8 %. Strain 4NS15T produces long chains of spores without a sporangium-like structure which can be distinguished from other Kibdelosporangium species. Isolate 4NS15T has a genome size of 10.35 Mbp with a G+C content of 68.1 mol%. Whole-cell hydrolysates of isolate 4NS15T are rich in meso-diaminopimelic acid and cell-wall sugars such as arabinose, galactose, glucose and ribose. Major fatty acids (>10 %) are C16 : 0, iso-C16 : 0 and iso-C15 : 0. The phospholipid profile contains diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylhydroxyethanolamine, aminolipid and glycoaminolipid. The predominant menaquinone is MK-9(H4). Based on its phenotypic and genotypic characteristics, isolate 4NS15T (NCCB 100701=CIP 111705=DSM 110728) merits recognition as representing a novel species of the genus Kibdelosporangium, for which the name Kibdelosporangium persicum sp. nov. is proposed.

Streptomonospora litoralis sp. nov., a halophilic thiopeptides producer isolated from sand collected at Cuxhaven beach.

Strain M2T was isolated from the beach of Cuxhaven, Wadden Sea, Germany, in course of a program to attain new producers of bioactive natural products. Strain M2T produces litoralimycin and sulfomycin-type thiopeptides. Bioinformatic analysis revealed a potential biosynthetic gene cluster encoding for the M2T thiopeptides. The strain is Gram-stain-positive, rod shaped, non-motile, spore forming, showing a yellow colony color and forms extensively branched substrate mycelium and aerial hyphae. Inferred from the 16S rRNA gene phylogeny strain M2T affiliates with the genus Streptomonospora. It shows 96.6% 16S rRNA gene sequence similarity to the type species Streptomonospora salina DSM 44593 T and forms a distinct branch with Streptomonospora sediminis DSM 45723 T with 97.0% 16S rRNA gene sequence similarity. Genome-based phylogenetic analysis revealed that M2T is closely related to Streptomonospora alba YIM 90003 T with a digital DNA-DNA hybridisation (dDDH) value of 26.6%. The predominant menaquinones of M2T are MK-10(H6), MK-10(H8), and MK-11(H6) (> 10%). Major cellular fatty acids are iso-C16:0, anteiso C17:0 and C18:0 10-methyl. The polar lipid profile consisted of diphosphatidylglycerol phosphatidyl glycerol, phosphatidylinositol, phosphatidylcholine, phosphatidylethanolamine, three glycolipids, two unknown phospholipids, and two unknown lipids. The genome size of type strain M2T is 5,878,427 bp with 72.1 mol % G + C content. Based on the results obtained from phylogenetic and chemotaxonomic studies, strain M2T (= DSM 106425 T = NCCB 100650 T) is considered to represent a novel species within the genus Streptomonospora for which the name Streptomonospora litoralis sp. nov. is proposed.

Mining Indonesian Microbial Biodiversity for Novel Natural Compounds by a Combined Genome Mining and Molecular Networking Approach.

Indonesia is one of the most biodiverse countries in the world and a promising resource for novel natural compound producers. Actinomycetes produce about two thirds of all clinically used antibiotics. Thus, exploiting Indonesia's microbial diversity for actinomycetes may lead to the discovery of novel antibiotics. A total of 422 actinomycete strains were isolated from three different unique areas in Indonesia and tested for their antimicrobial activity. Nine potent bioactive strains were prioritized for further drug screening approaches. The nine strains were cultivated in different solid and liquid media, and a combination of genome mining analysis and mass spectrometry (MS)-based molecular networking was employed to identify potential novel compounds. By correlating secondary metabolite gene cluster data with MS-based molecular networking results, we identified several gene cluster-encoded biosynthetic products from the nine strains, including naphthyridinomycin, amicetin, echinomycin, tirandamycin, antimycin, and desferrioxamine B. Moreover, 16 putative ion clusters and numerous gene clusters were detected that could not be associated with any known compound, indicating that the strains can produce novel secondary metabolites. Our results demonstrate that sampling of actinomycetes from unique and biodiversity-rich habitats, such as Indonesia, along with a combination of gene cluster networking and molecular networking approaches, accelerates natural product identification.

Genetic engineering approaches for the fermentative production of phenylglycines.

L-phenylglycine (L-Phg) is a rare non-proteinogenic amino acid, which only occurs in some natural compounds, such as the streptogramin antibiotics pristinamycin I and virginiamycin S or the bicyclic peptide antibiotic dityromycin. Industrially, more interesting than L-Phg is the enantiomeric D-Phg as it plays an important role in the fine chemical industry, where it is used as a precursor for the production of semisynthetic ß-lactam antibiotics. Based on the natural L-Phg operon from Streptomyces pristinaespiralis and the stereo-inverting aminotransferase gene hpgAT from Pseudomonas putida, an artificial D-Phg operon was constructed. The natural L-Phg operon, as well as the artificial D-Phg operon, was heterologously expressed in different actinomycetal host strains, which led to the successful production of Phg. By rational genetic engineering of the optimal producer strains S. pristinaespiralis and Streptomyces lividans, Phg production could be improved significantly. Here, we report on the development of a synthetic biology-derived D-Phg pathway and the optimization of fermentative Phg production in actinomycetes by genetic engineering approaches. Our data illustrate a promising alternative for the production of Phgs.

Comparative statistical component analysis of transgenic, cyanophycin-producing potatoes in greenhouse and field trials.

Potatoes are a promising system for industrial production of the biopolymer cyanophycin as a second compound in addition to starch. To assess the efficiency in the field, we analysed the stability of the system, specifically its sensitivity to environmental factors. Field and greenhouse trials with transgenic potatoes (two independent events) were carried out for three years. The influence of environmental factors was measured and target compounds in the transgenic plants (cyanophycin, amino acids) were analysed for differences to control plants. Furthermore, non-target parameters (starch content, number, weight and size of tubers) were analysed for equivalence with control plants. The huge amount of data received was handled using modern statistical approaches to model the correlation between influencing environmental factors (year of cultivation, nitrogen fertilization, origin of plants, greenhouse or field cultivation) and key components (starch, amino acids, cyanophycin) and agronomic characteristics. General linear models were used for modelling, and standard effect sizes were applied to compare conventional and genetically modified plants. Altogether, the field trials prove that significant cyanophycin production is possible without reduction of starch content. Non-target compound composition seems to be equivalent under varying environmental conditions. Additionally, a quick test to measure cyanophycin content gives similar results compared to the extensive enzymatic test. This work facilitates the commercial cultivation of cyanophycin potatoes.

A Complex Signaling Cascade Governs Pristinamycin Biosynthesis in Streptomyces pristinaespiralis.

Pristinamycin production in Streptomyces pristinaespiralis Pr11 is tightly regulated by an interplay between different repressors and activators. A γ-butyrolactone receptor gene (spbR), two TetR repressor genes (papR3 and papR5), three SARP (Streptomyces antibiotic regulatory protein) genes (papR1, papR2, and papR4), and a response regulator gene (papR6) are carried on the large 210-kb pristinamycin biosynthetic gene region of Streptomyces pristinaespiralis Pr11. A detailed investigation of all pristinamycin regulators revealed insight into a complex signaling cascade, which is responsible for the fine-tuned regulation of pristinamycin production in S. pristinaespiralis.

Identification of two-component system AfsQ1/Q2 regulon and its cross-regulation with GlnR in Streptomyces coelicolor.

The two-component system AfsQ1/Q2 of Streptomyces coelicolor was identified in our previous work as a pleiotropic regulator for antibiotic biosynthesis and morphological differentiation under the condition of a minimal medium supplemented with 75 mM glutamate. In this work, we report the dissection of the mechanism underlying the function of AfsQ1/Q2 on antibiotic production and also the identification of the AfsQ1/Q2 regulon. The results showed that AfsQ1/Q2 stimulated antibiotic ACT, RED and CDA production directly through the pathway-specific activator genes actII-ORF4, redZ and cdaR respectively. In addition, expression of sigQ that encodes a sigma factor and is divergently transcribed from afsQ1 was also subject to direct regulation by AfsQ1/Q2. The precise AfsQ1 binding sites in the upstream regions of these target genes were determined by DNase I footprinting assays coupled with site-directed DNA mutagenesis. By computational prediction and functional analysis, at least 17 new AfsQ1 targets were identified, including pstS gene encoding a high-affinity phosphate-binding protein and two developmental genes whiD, bldM. For the AfsQ1/Q2 regulon, an AfsQ1 binding motif comprising the sequence GTnAC-n(6) -GTnAC has been defined. Interestingly, we found from electrophoretic mobility shift assays and transcriptional analysis that AfsQ1/Q2 can also function as a repressor for nitrogen assimilation, and AfsQ1 can compete with GlnR for the promoter regions of glnA and nirB, suggesting the cross-regulation between AfsQ1/Q2 and GlnR in nitrogen metabolism. These findings suggested that AfsQ1/Q2 is important not only for antibiotic biosynthesis but also in maintaining the metabolic homeostasis of nutrient utilization under the stress of high concentration of glutamate in S. coelicolor.

Streptogramins - two are better than one!

Streptogramins are potent drugs against numerous highly resistant pathogens and therefore are used as antibiotics of last-resort human therapy. They consist of a mixture of two different types of chemical substances - the group A streptogramins, which are polyunsaturated macrolactones, and the group B streptogramins, representing cyclic hexadepsipeptides. Streptogramins are unique in their mode of action: each component alone exhibits a moderate bacteriostatic activity by binding to the bacterial 50S ribosomal subunit and thereby blocking translation, whereas the synergic combination of both substances is up to hundred fold more effective than the single compounds, resulting in a bactericidal activity. The streptogramin biosynthetic genes are organized as large antibiotic superclusters. These clusters harbour numerous regulatory genes, which encode different types of regulators that together form a complex hierarchical signalling system, which governs the regulation of streptogramin biosynthesis. Resistance is also regulated by this cascade. However, whereas resistance against streptogramins is quite well understood in diverse pathogenic organisms, only little is known about how the natural producer strains protect themselves against these toxic compounds. Here, we give an overview about the recent advances in streptogramin investigations with a main focus on the best-studied representatives, pristinamycin and virginiamycin. We concentrate on the biosynthesis of these compounds, their regulation and resistance determinants as well as their application in medicine and food industry.

Extracting regulator activity profiles by integration of de novo motifs and expression data: characterizing key regulators of nutrient depletion responses in Streptomyces coelicolor.

Determining transcriptional regulator activities is a major focus of systems biology, providing key insight into regulatory mechanisms and co-regulators. For organisms such as Escherichia coli, transcriptional regulator binding site data can be integrated with expression data to infer transcriptional regulator activities. However, for most organisms there is only sparse data on their transcriptional regulators, while their associated binding motifs are largely unknown. Here, we address the challenge of inferring activities of unknown regulators by generating de novo (binding) motifs and integrating with expression data. We identify a number of key regulators active in the metabolic switch, including PhoP with its associated directed repeat PHO box, candidate motifs for two SARPs, a CRP family regulator, an iron response regulator and that for LexA. Experimental validation for some of our predictions was obtained using gel-shift assays. Our analysis is applicable to any organism for which there is a reasonable amount of complementary expression data and for which motifs (either over represented or evolutionary conserved) can be identified in the genome.

Genome sequence of the bialaphos producer Streptomyces sp. DSM 41527 and two putative phosphonate antibiotic producers Streptomyces sp. DSM 41014 and DSM 41981 from the DSMZ strain collection.

Streptomyces sp. DSM 41014, DSM 41527, and DSM 41981 are three strains from the DSMZ strain collection. Here, we present the draft genome sequences of DSM 41014, DSM 41527, and DSM 41981 with a size of 9.09 Mb, 8.45 Mb, and 9.23 Mb, respectively.

Biotechnological and pharmaceutical potential of twenty-eight novel type strains of Actinomycetes from different environments worldwide.

Actinomycetes are a prolific source of bioactive natural compounds many of which are used as antibiotics or other drugs. In this study we investigated the genomic and biochemical diversity of 32 actinobacterial strains that had been deposited at the DSMZ-German Collection of Microorganisms and Cell Cultures decades ago. Genome-based phylogeny and in silico DNA-DNA hybridization supported the assignment of these strains to 26 novel species and two novel subspecies and a reclassification of a Streptomyces species. These results were consistent with the biochemical, enzymatic, and chemotaxonomic features of the strains. Most of the strains showed antimicrobial activities against a range of Gram-positive and Gram-negative bacteria, and against yeast. Genomic analysis revealed the presence of numerous unique biosynthetic gene clusters (BGCs) encoding for potential novel antibiotic and anti-cancer compounds. Strains DSM 41636T and DSM 61640T produced the antibiotic compounds A33853 and SF2768, respectively. Overall, this reflects the significant pharmaceutical and biotechnological potential of the proposed novel type strains and underlines the role of prokaryotic systematics for drug discovery. In order to compensate for the gender gap in naming prokaryotic species, we propose the eponyms for all newly described species to honour female scientists.

Challenging old microbiological treasures for natural compound biosynthesis capacity.

Strain collections are a treasure chest of numerous valuable and taxonomically validated bioresources. The Leibniz Institute DSMZ is one of the largest and most diverse microbial strain collections worldwide, with a long tradition of actinomycetes research. Actinomycetes, especially the genus Streptomyces, are renowned as prolific producers of antibiotics and many other bioactive natural products. In light of this, five Streptomyces strains, DSM 40971T, DSM 40484T, DSM 40713T, DSM 40976T, and DSM 40907T, which had been deposited a long time ago without comprehensive characterization, were the subject of polyphasic taxonomic studies and genome mining for natural compounds based on in vitro and in silico analyses. Phenotypic, genetic, and phylogenomic studies distinguished the strains from their closely related neighbors. The digital DNA-DNA hybridization and average nucleotide identity values between the five strains and their close, validly named species were below the threshold of 70% and 95%-96%, respectively, determined for prokaryotic species demarcation. Therefore, the five strains merit being considered as novel Streptomyces species, for which the names Streptomyces kutzneri sp. nov., Streptomyces stackebrandtii sp. nov., Streptomyces zähneri sp. nov., Streptomyces winkii sp. nov., and Streptomyces kroppenstedtii sp. nov. are proposed. Bioinformatics analysis of the genome sequences of the five strains revealed their genetic potential for the production of secondary metabolites, which helped identify the natural compounds cinerubin B from strain DSM 40484T and the phosphonate antibiotic phosphonoalamide from strain DSM 40907T and highlighted strain DSM 40976T as a candidate for regulator-guided gene cluster activation due to the abundance of numerous "Streptomyces antibiotic regulatory protein" (SARP) genes.

Biotransformation-coupled mutasynthesis for the generation of novel pristinamycin derivatives by engineering the phenylglycine residue.

Streptogramins are the last line of defense antimicrobials with pristinamycin as a representative substance used as therapeutics against highly resistant pathogenic bacteria. However, the emergence of (multi)drug-resistant pathogens renders these valuable antibiotics useless; making it necessary to derivatize compounds for new compound characteristics, which is often difficult by chemical de novo synthesis due to the complex nature of the molecules. An alternative to substance derivatization is mutasynthesis. Herein, we report about a mutasynthesis approach, targeting the phenylglycine (Phg) residue for substance derivatization, a pivotal component of streptogramin antibiotics. Mutasynthesis with halogenated Phg(-like) derivatives altogether led to the production of two new derivatized natural compounds, as there are 6-chloropristinamycin I and 6-fluoropristinamycin I based on LC-MS/MS analysis. 6-Chloropristinamycin I and 6-fluoropristinamycin I were isolated by preparative HPLC, structurally confirmed using NMR spectroscopy and tested for antimicrobial bioactivity. In a whole-cell biotransformation approach using an engineered E. coli BL21(DE3) pET28-hmo/pACYC-bcd-gdh strain, Phg derivatives were generated fermentatively. Supplementation with the E. coli biotransformation fermentation broth containing 4-fluorophenylglycine to the pristinamycin mutasynthesis strain resulted in the production of 6-fluoropristinamycin I, demonstrating an advanced level of mutasynthesis.

The bifunctional role of aconitase in Streptomyces viridochromogenes Tü494.

In many organisms, aconitases have dual functions; they serve as enzymes in the tricarboxylic acid cycle and as regulators of iron metabolism. In this study we defined the role of the aconitase AcnA in Streptomyces viridochromogenes Tü494, the producer of the herbicide phosphinothricyl-alanyl-alanine, also known as phosphinothricin tripeptide or bialaphos. A mutant in which the aconitase gene acnA was disrupted showed severe defects in morphology and physiology, as it was unable to form any aerial mycelium, spores nor phosphinothricin tripeptide. AcnA belongs to the iron regulatory proteins (IRPs). In addition to its catalytic function, AcnA plays a regulatory role by binding to iron responsive elements (IREs) located on the untranslated region of certain mRNAs. A mutation preventing the formation of the [4Fe-4S] cluster of AcnA eliminated its catalytic activity, but did not inhibit RNA-binding ability. In silico analysis of the S. viridochromogenes genome revealed several IRE-like structures. One structure is located upstream of recA, which is involved in the bacterial SOS response, and another one was identified upstream of ftsZ, which is required for the onset of sporulation in streptomycetes. The functionality of different IRE structures was proven with gel shift assays and specific IRE consensus sequences were defined. Furthermore, RecA was shown to be upregulated on post-transcriptional level under oxidative stress conditions in the wild-type strain but not in the acnA mutant, suggesting a regulatory role of AcnA in oxidative stress response.

A novel GlnR target gene, nnaR, is involved in nitrate/nitrite assimilation in Streptomyces coelicolor.

GlnR is the global transcriptional regulator of nitrogen assimilation in Streptomyces coelicolor. Under nitrogen starvation, GlnR controls the transcription of at least nine genes associated with nitrogen metabolism. In this study, we identified a new GlnR target gene, SCO2958, named nnaR (nitrate/nitrite assimilation regulator). In silico analysis of NnaR revealed the presence of two distinct domains: an N-terminal uroporphyrinogen-III synthase (HemD)-like enzymatic domain and a C-terminal DNA binding domain. Complementation experiments with a haemin auxotroph Escherichia coli ΔhemD mutant strain revealed that NnaR has no HemD activity. Physiological studies of an S. coelicolor nnaR : : Tn5062 mutant showed that NnaR is involved in regulating nitrite reduction. By electrophoretic mobility shift assays the functionality of the NnaR DNA binding domain was confirmed, and it was found that NnaR binds in front of the genes narK (putative nitrate extrusion protein), nirB (nitrite reductase), nirA (putative nitrite/sulphite reductase) and nasA (putative nitrate reductase), which are associated with nitrate/nitrite assimilation. Furthermore, a cooperative binding of NnaR together with GlnR to the nirB promoter was observed, suggesting that NnaR may act as a GlnR co-activator.

Ψ-Footprinting approach for the identification of protein synthesis inhibitor producers.

Today, one of the biggest challenges in antibiotic research is a targeted prioritization of natural compound producer strains and an efficient dereplication process to avoid undesired rediscovery of already known substances. Thereby, genome sequence-driven mining strategies are often superior to wet-lab experiments because they are generally faster and less resource-intensive. In the current study, we report on the development of a novel in silico screening approach to evaluate the genetic potential of bacterial strains to produce protein synthesis inhibitors (PSI), which was termed the protein synthesis inhibitor ('psi') target gene footprinting approach = Ψ-footprinting. The strategy is based on the occurrence of protein synthesis associated self-resistance genes in genome sequences of natural compound producers. The screening approach was applied to 406 genome sequences of actinomycetes strains from the DSMZ strain collection, resulting in the prioritization of 15 potential PSI producer strains. For twelve of them, extract samples showed protein synthesis inhibitory properties in in vitro transcription/translation assays. For four strains, namely Saccharopolyspora flava DSM 44771, Micromonospora aurantiaca DSM 43813, Nocardioides albertanoniae DSM 25218, and Geodermatophilus nigrescens DSM 45408, the protein synthesis inhibitory substance amicoumacin was identified by HPLC-MS analysis, which proved the functionality of the in silico screening approach.